Another suggestion.
It might be worthwhile being able to declare that the
elements and data inside an element should be treated as
atomic, as a normal form. This would help relational implementations.
For example, to say that the following instance:
<example>
<name><img src="prince.gid"/></name>
<formula>1<sub>2</sub></formula>
</example>
the name and formula element types should be treated as atomic.
The database should store the contents as well-formed XML entity:
<img src="prince.gid"/>
and
1<sub>2</sub>
Rick Jelliffe